This reviews the Article A Measurement of g Using Alexander's Diving Bell which appeared in The Physics Teacher Vol 48, September 2010, by M. Quiroga, S. Martinez, and S. Otranto.
Since the Earth's gravitational attraction, g is defined by F = mg, where m is some mass and F the weight of that mass, we can determine a value by measuring F and m. That can be done with a known mass and an accurate force measuring device, such as a well-calibrated spring. (It can NOT be done with a balance, which simpliy compares one mass to another.)
Here that is done by forcing an air filled tube with an open bottom down into water. As the tube is pushed deeper, the water pressure causes the air in the tube to be compressed, allowing water to rise into the tube. The amount of air in the tube remains constant, but it is compressed, serving as a well-calibrated spring. The depth of water is measured, and gives the effective mass.
I like this style of experiment, because it uses little equipment, all readily available, and makes the principles at work visible, with no complexity to obscure them.
Since the Earth's gravitational attraction, g is defined by F = mg, where m is some mass and F the weight of that mass, we can determine a value by measuring F and m. That can be done with a known mass and an accurate force measuring device, such as a well-calibrated spring. (It can NOT be done with a balance, which simpliy compares one mass to another.)
Here that is done by forcing an air filled tube with an open bottom down into water. As the tube is pushed deeper, the water pressure causes the air in the tube to be compressed, allowing water to rise into the tube. The amount of air in the tube remains constant, but it is compressed, serving as a well-calibrated spring. The depth of water is measured, and gives the effective mass.
I like this style of experiment, because it uses little equipment, all readily available, and makes the principles at work visible, with no complexity to obscure them.
Morris Hirsch Oct 4 2010